It was quite chilly in Oxfordshire, UK, today. Yesterday we had a glorious English late summer day with mid-afternoon temperatures in the high 20s. What a contrast today with temperatures a full 10 degrees lower at around 15 degrees mid morning! So, when I went outside with bare arms first thing I got goosebumps!
My deal old body was trying to protect me from heat-loss by making the hairs on my arms fluff up and act as better insulators by trapping a layer of warmed-up air next to my skin and reducing the heat loss due to airflow!
What on earth was it thinking of? I don't have hairy arms - well not so's you'd notice. What hairs I do have are short, fine and sparse, so useless as an insulator, whether fluffed up or laying down. What they are good for though is detecting any unwanted small wild-life which might be strolling about on my arms. They do this because they have a sensitive nerve-ending in the hair follicle which detects tiny local movements. This is probably one reason we haven't got rid of body hair altogether.
So why did my hair try to fluff up?
Because we still have the same mechanism which our earlier, hairy, ancestors had, just like the other apes have, and just like many other mammals such as cats and dogs have, and just like many birds have with respect to their feathers. Our skin detects coldness and initiates a nerve reflex known as arasing, piloerection, or the pilomotor reflex. This causes tiny muscles called arrector pili, attached to the base of each hair follicle, to contract and so pull the normally slanting follicle more upright. It all happens automatically with no conscious thought on our part. Other causes of the reflex can be fear, sexual arousal, even nostalgia and euphoria.
As well as protecting them from cold, in other mammals, having big hair can also make them look bigger, more powerful or more aggressive. In humans, it is utterly useless. It serves no useful purpose because we have lost most of our body hair during the last few million years of our evolution. We probably lost it to help with heat-dissipation when hunting down running animals or to improve sweat evaporation - which amounts to the same thing really.
But what we haven't lost is the nerve-endings, nerve pathways that provide the reflex, and muscles which pull the hairs upright because there was nothing to be gained by losing them as the cost of retaining them is minimal. There is nothing to drive their loss because losing them would not give us any particular advantage over others of our species who kept them, so there was nothing for natural selection to select.
So, what we get now is goosebumps, as the pulling of the arrector pili muscles causes little bumps to form on our skin where the other end of the muscle is attached.
It goes without saying that this system wasn't intelligently designed of course. It is completely without logical explanation if the human body was intelligently designed. It makes perfect sense as the product of evolution, as I've explained above.
So, next time you get goosebumps, look at it as your body trying to show you how you evolved from the common ancestor of many other mammals over many millions of years and that there was no intelligence involved. You really weren't made from a lump of dirt or dust; you have been perfected by natural forces and are the direct descendent of survivors who passed the fitness test at every generation and never once failed to breed - for three and a half billion years.
That thought should give you goosebumps.